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Semi-Automatic Measurement of the Airway Dimension by Computed Tomography Using the Full-Width-Half- Maximum Method: a Study on the Measurement Accuracy according to the CT Parameters and Size of the Airway

Objective: To assess the influence of variable factors such as the size of the
airway and the CT imaging parameters such as the reconstruction kernel, field-ofview
(FOV), and slice thickness on the automatic measurement of airway dimension.
Materials and Methods: An airway phantom was fabricated that contained
eleven poly-acryl tubes of various lumen diameters and wall thicknesses. The
measured density of the poly-acryl wall was 150 HU, and the measured density of
the airspace filled with polyurethane foam was 900 HU. CT images were
obtained using a 16-MDCT (multidetector CT) scanner and were reconstructed
with various reconstruction kernels, thicknesses and FOV. The luminal radius
and wall thickness were measured using in-house software based on the fullwidth-
half-maximum method. The measured values as determined by CT and the
actual dimensions of the tubes were compared.
Results: Measurements were most accurate on images reconstructed with use
of a standard kernel (mean error: 0.03+-0.21 mm for wall thickness and 0.12
0.11 mm for the luminal radius). There was no significant difference in accuracy
among images with the use of variable slice thicknesses or a variable FOV.
Below a 1-mm threshold, the measurement failed to represent the change of the
real dimensions.
Conclusion: Measurement accuracy was strongly influenced by the specific
reconstruction kernel utilized. For accurate measurement, standardization of the
imaging protocol and selection of the appropriate anatomic level are essential.